Most fluxes and defluxing chemicals used by industry to manufacture electronic circuits, such as military hardware, are either contributing to ozone depletion of the atmosphere or are considered by local environmental agencies, such as the Air Quality Management District in the Los Angeles basin, as environmental pollutants or health hazards. For example, it has been reported that if CFCs (chlorofluorohydrocarbons), which are used in vapor degreasing to clean soldered parts where a rosin flux is employed, are released to the atmosphere, they will remain there as an ozone depletant for nearly 100 years. Other chemicals such as rosin fluxes, alcohols, and the like pose health risks and disposal problems for industry.
Water-soluble fluxes could be the simple solution for this major problem. However, most water-soluble fluxes are formulated with harsh activators, such as hydrochloric acid and complex glycols, which create major cleaning and residue problems for the printed circuit board and the electrical circuitry thereon and which tend to severely corrode the metal being soldered or contaminate the dielectric, causing a tendency for electromigration. Other water-soluble fluxes are formulated with iso-propanol and/or plasticizers, which create disposal and health problems.
Water-soluble solder pastes are formulations that combine a soldering alloy, typically in powder form, with a water-soluble organic activator and a water-soluble organic vehicle; see, e.g., U.S. Pat. No. 4,872,928. While citric acid is mentioned as an example of an organic acid that acts as an activator, the paste also includes other materials that are not environmentally desirable, such as polyethylene glycol.
What is desired is a simple, non-toxic, non-corrosive, environmentally-safe liquid soldering paste that produces solder joints of high metallic luster and excellent quality.